March 21, 2024

expert reaction to conference abstracts about sweeteners and weight loss control / weight maintenance

Scientists react to obesity conference abstracts about sweeteners and weight loss control. 

Prof Kevin McConway, Emeritus Professor of Applied Statistics, Open University, said:

“It’s one of the times of year when big scientific conferences occur, and so journalists and scientific commenters (like me) are faced with press releases on studies we can’t evaluate properly, because we just don’t get enough information.  There is an abstract of a presentation that hasn’t happened yet, and a press release.  But most details are missing.  With most types of study, particularly those involving clinical trials (like this one), or systematic reviews or observational studies, the devil is in the detail, which we haven’t seen.  It’s impossible to make a proper evaluation of the quality of the study’s conclusions without seeing more detail.  We can’t even rely on there having been a peer review process.  Usually (as here) the abstract of the presentation will have been through a review by the conference organisers, but they won’t have seen all the detail either.  So I’m not going to waste my time and yours speculating about exactly what has been learned from this study.

“For this particular study, the press release and the abstracts of the presentations are rather fuller than they sometimes are, so there is something to go on, but it really can’t do more than suggest that there might be something useful and interesting in the full research report, when we get to see it.  Some results are given, though not every important detail.  So, for example, we learn that the drop-out rate for the study was larger than expected.  That might or might not be concerning.  Detail on why and when people dropped out might tell us something about how acceptable the different diets were, or on whether some feature of the intervention caused problems for some participants – but we don’t know that.

“One thing that we do know is that this study followed good practice by publishing a protocol in advance.  In principle, that allows us to check whether the researchers did what they intended to do, and if not, why they didn’t.  Changes to these protocols do happen reasonably often, usually for perfectly good reasons.  The full report should give reasons for any changes and explain their consequences – but again we don’t have that.  One possible change, that might have consequences, relates to the safety aspects of the trial – but it’s not even clear yet whether there was a change or not.  More on that below.

“The press release also says something interesting about the possible motivation for the trial.  It refers to a 2023 systematic review by WHO of the health effects of non-sugar sweeteners.  To summarise very crudely, that review found evidence from short-term clinical trials that using non-sugar sweeteners could be associated with lowering body weight, BMI total calorie intake and sugar intake, without much evidence of impact on disease diagnosis.  But in data from observational studies, usually longer term, there was some evidence that BMI increased rather than decreasing with more use of non-sugar sweeteners, as well as increases in the risk of some diseases, particularly type 2 diabetes and cardiovascular disease.  But the quality of the evidence behind most of these findings wasn’t high, particularly those from observational studies (which provided most of the evidence of possible harms).  That review’s findings were fairly controversial at the time.

“The press release implies that one of the reasons for the new trial is to deal with these shortcomings of the WHO review – or, at any rate, that we should reconsider the WHO findings in the light of the trial results.  But I’m not sure that we can do that – though again I’ll have to wait for the full trial report to be sure.

“One issue is that the new trial gets its data from a specific scenario.  The participants began their involvement by two months of trying to lose at least 5 per cent of their body weight.  Then the trial looked at how people’s success in maintaining their weight loss, over another 10 months, was associated with whether they had access to non-sugar sweeteners and sweetness enhancers.  This does certainly seem to be something worth looking at, but the results will say something directly only about that situation of maintaining weight loss, after a period of quite rapid weight loss.  What, if anything, this says about the use of non-sugar sweeteners for weight reduction in the first place isn’t clear, to me at least.  Also this scenario is unlike what happened in most of the studies reviewed by WHO – so these new findings might well add to what WHO concluded, but won’t supersede it, I’d say.

“I’m a bit more concerned about the safety aspects.  The negative associations, found by WHO, between consumption of non-sugar sweeteners and the risk of some diseases, were found only in observational studies and generally only after differences in sweetener use had gone on for some considerable time.  Is the length of this new trial long enough for associations with disease risk to show up?  The protocol for the new trial says that these safety aspects would be measured primarily by measuring the populations of bacteria and microorganisms in the guts of the participants (the so-called gut microbiota).  There would also be secondary measures of risk markers in the body for type 2 diabetes and cardiovascular disease (CVD).  But nothing at all is said in the abstracts or the press release about microbes in the gut.  Why not?  This was the pre-registered measure of safety.  Did they have to change this, and if so why?  We aren’t told.  Something is said about risk markers for diabetes and CVD – but only briefly.  We are told that these markers did not differ between the participants who had access to the non-sugar sweeteners and those who did not – but only in those people who completed all the clinical investigations, and about a quarter of the participants did not complete them all.  It’s quite possible that that doesn’t matter, but we can’t tell without more detail.  Also, what’s more interesting than markers for diabetes and CVD is actual diagnoses of diabetes and CVD – but those diseases take time to develop, and the length of this trial might not be enough to show whether the risk increased or not.

“In brief, it’s not clear whether this new trial can help to confirm or disconfirm the findings from that WHO review.  The actual scenario it investigated is different from most of those reviewed by WHO, and what we know from the new trial about differences in disease risk really isn’t very clear (and is barely discussed in the information we have so far).  We might know more after the full results are published, but now, it’s just too soon to say.”

First conference abstract title: ‘Effect of sweeteners and sweetness enhancers on weight loss maintenance in adults and children with overweight or obesity – results from the SWEET multicentre, randomised, controlled, trial’ by Anne Raben et al.

Second conference abstract title: ‘The impact of sweeteners on eating behaviours during a weight maintenance RCT in adults and children with overweight: SWEET project’ by Clarissa Dakin et al.

This was under embargo until 23:01 UK time on Thursday 21 March 2024.

There are no full papers and the conference abstracts are not peer reviewed.

Declared interests

Prof Kevin McConway: “I am a Trustee of the SMC and a member of its Advisory Committee.  My quote above is in my capacity as an independent professional statistician.”